The Sensibility of Rocking Motion of Flat-Bottom Cylindrical Shell Tanks to Sloshing Motion

This paper examines the sensibility of rock motion of flat-bottom cylindrical shell tanks to the lateral force induced by the sloshing motion. Since the natural period of sloshing motion of the tank may be close to that of rocking motion of the tank, their resonance may result the serious damages of the storage systems. Therefore, it is necessary to examine their fundamental behavior beforehand. Using horizontal sinusoidal ground motion whose period matches the natural period of 1st sloshing mode of the tank, the rocking motion of the tank is numerically examined. The results imply that the sloshing behavior has the potential to make tanks rock.

Blowdown/Jet Impingement Force-Time History

The approximate blowdown/jet impingement force resulting from the rupture of a pipe into a low back pressure receiver is presented. The pipe fluid is an ideal gas flowing under isentropic conditions. Initial flow with Mach numbers up to 0.25 is considered. Solution of the governing thermal hydraulic equations is by the method of characteristics and application is by a wave diagram.

Peridynamic Modeling of Impact Damage

The peridynamic theory is an alternative formulation of continuum mechanics oriented toward modeling discontinuites such as cracks. It differs from the classical theory and most nonlocal theories in that it does not involve spatial derivatives of the displacement field. Instead, it is formulated in terms of integral equations, whose validity is not affected by the presence of discontinuities such as cracks. It may be thought of as a “continuum version of molecular dynamics” in that particles interact directly with each other across a finite distance. This paper outlines the basis of the peridynamic theory and its numerical implementation in a three-dimensional code called EMU. Examples include simulations of a Charpy V-notch test, accumulated damage in concrete due to multiple impacts, and crack fragmentation of a glass plate.

Investigation of Steam Desuperheater Waterhammer

Steam supplied to an underground piping distribution network from a fossil fired boiler is desuperheated using water injection valves. Waterhammers occurred in the system, failing a valve on two separate occasions. Operations personnel also experience excessive high-level alarms at drain stations local to the valves. An investigation was conducted to determine the root cause of the valve failures and the cause of the excessive water in the steam system. Mitigating design changes were also proposed to solve these problems. Available analytical methods were shown to be effective in predicting waterhammer occurrence and magnitude. These methods can be used to evaluate the potential for waterhammer in similar systems with potential steam/water interaction.

Stratified Flow Experiments Pertaining to Advanced LWR Reactor Passive Safety System Designs

During a loss-of-coolant-accident in advanced light water reactors, outside coolant enters the cold leg by gravity to cool the core. This coolant is at a substantially lower temperature and thus is heavier than the liquid in and from the reactor. Consequently, stratified flow may occur. A stratified flow may cause condensation-induced water hammer, and will influence the coolant flow behavior. Two sets of experiments are in progress to better understand stratified flow conditions that lead to water hammer, and the density stratification behavior. The first set uses air-oil-water as the test media. Its purposes are to conduct exploratory tests and to provide instruction an apparatus for education purposes. The second set of tests will use steam and water and, later, the refrigerant R123. This paper describes the exploratory test facility, gives a brief description of the facility that will be used for the steam-water and refrigerant tests, describes the overall test plan, and finally gives some preliminary results on the intrusion of a lighter liquid into a pipe against flow.

A Simple Predictive Method of Steam Pipe Forces From Stop Valve Closure

Piping systems that are subject to a fast closing valve are susceptible to large steamhammer forces. The steamhammer force is a result of high-speed pressure waves propagating through the pipe that create sizeable pressure gradients in the pipe. This paper introduces a simple predictive method of the pipe forces induced by the pressure gradients in a steam pipe resulting from stop valve closure. The case of instant valve closure is also examined for comparison. The assumptions in this analysis are that the stop valve closure is linear, the pressure losses from any bends in the pipe can be ignored, the downstream pressure is constant, the steam flow is at a constant pressure, and finally the pipe walls are rigid at a constant radius. The method introduces functions that are constant along diagonal lines on the time-space graph. The pressure and velocity along these lines can be computed from the initial conditions and boundary conditions. Finally, the pipe forces are calculated using the pressures in the targeted regions of the pipe.

Underwater Explosion in a Pool and Damage Assessment: A Global Approach From Far-Field to Close Range

The concern of this paper is the study of the effects of the detonation produced by an underwater explosive device. This work applies in particular to the study of some industrial pools, filled with water and a few meters deep. These pools are generally build so as to ensure a certain watertightness, this function being obtained for instance by the adjunction of an internal liner, a few millimeters thick and made of stainless steel. Here, we focus on the possible loss of this function both by the damage caused to concrete and the perforation of the liner. Those damages could be either due on one hand to the local deformations related to the global structure response and on the other hand to the local effects of the explosion. The first aspect has been investigated previously, using in particular the so-called “Method of Images (MOI)” (F. Delmaire-Sizes et al, 2001). The second aspect only occurs when the device is in a sufficiently close range so that the pressures produced by the detonation can cause volumetric damage into the materials. The starting point of this second phenomenon is investigated in the paper on the basis of a numerical model for concrete under high pressure and high strain rates (T. J. Holmquist, 1993). The second phenomenon comes in addition with the first one. An example is conducted showing how numerical simulations for the local analysis, coupling Eulerian and Lagrangian computations, complete the previous global analysis.

Numerical Simualtion of Turbulence Mixing Characteristic in Various Secondary Flow Conditions at T-Junction Piping Systems

Temperature fluctuation caused by mixing the fluids with different temperature in a T-junction pipe gives eventually thermal fatigue to structure, and this phenomenon is significant as safety issue in liquid metal cooled fast reactor (LMFBR). In Japan Nuclear Cycle Development Institute (JNC), experimental and numerical investigations have been performed to clarify the mixing phenomena in the T-junction pipe and to establish an evaluation rule for design. If the T-junction pipe is set near an elbow pipe, turbulence mixing is surly affected by the secondary flow generated in the elbow pipe and it is necessary to study the influence of the secondary flow on the temperature fluctuation in the T-junction pipe. We carried out investigation into the secondary flow effect by numerical simulation using a quasi-direct numerical simulation code. Numerical simulation is conducted on the existing experiment, in which the test section simulated the T-junction pipe with the elbow pipe in LMFBR. Major parameter in the numerical simulation is the flow direction of the branch pipe to the flow direction of the elbow pipe. We discuss the influences of the secondary flow on turbulent mixing behavior, and also clarify the mixing mechanism in T-junction pipe.

Discrete Element Method for Modeling Penetration

The Discrete Element Method (DEM) discretizes a material using rigid elements of simple shape. Each element interacts with neighboring elements through appropriate interaction laws. The number of elements is typically large and is limited by computer speed. The method has seen widespread applications to modeling particulate media and more recently to modeling solids such as concrete, ceramic, and metal. For problems with severe damage, DEM offers a number of attractive features over continuum based numerical methods, with the primary feature being a seamless transition from solid phase to particulate phase. This study illustrates the potential of DEM for modeling penetration and briefly points out its numerous advantages. A weakness of DEM is that its convergence properties are not understood. The crucial question is whether convergence is obtained as DEM element size vanishes in the limit of model refinement. The major focus of our investigation will be a careful study of convergence for modeling the degradation of a solid into fragments. Our results show that indeed convergence is obtained in several specific test problems. Moreover, elastic interelement stiffness and damping properties were proven to be particle size-independent. However, convergence in material failure due to crack growth is obtained only if the interparticle potentials are properly constructed as functions of DEM element size and bulk material properties such as elastic modulus and fracture toughness.

Strength Estimates for High Velocity Penetration of Geological Targets by the Compaction Ring Theory

Existing theories for rigid body penetration model the target response to a penetration process as a cavity-expansion. A new analysis, however, offers an innovative approach to rigid body penetration of porous geological targets. The theory analyzes the formation of a compacted ring of target material observed around the boreholes in recovered targets. Applying fundamental laws of motion to an element during the formation of the ring leads to estimates for the three stresses that control the penetration event. A retarding force on the projectile nose is derived and then used to arrive at an estimate for penetration depth. The penetration depth equation, resulting from this model, is dependent upon known projectile properties, target material properties, and the impact velocity. Neglected are the effects of friction and shear. The solving procedure returns an estimate for the target yield strength. The model can then be used to predict the penetration of any penetrator into the target material. The results are promising and in agreement with the experimental observations.